Digestive System Model Written description by Sue McKee for Let’s Talk Science in Ottawa The activity part of this was adapted from an activity by Aaron Lichtig; West Riviera Magnet Elementary School, Riviera Beach, Palm Beach. This activity links to the Grade 5 Life Systems strand – Human Organ Systems. Big Ideas • Organ systems are components of a larger system (the body) and, as such, work together and affect one another. (Overall expectations 2 and 3) • Organ structures are linked to their functions. (Overall expectations 2 and 3) • Systems in the human body work together to meet our basic needs. (Overall expectations 2 and 3) and somewhat to: • Choices we make affect our organ systems and, in turn, our overall health. (Overall expectations 1 and 3) Overall expectations 1. analyse the impact of human activities and technological innovations on human health; 2. investigate the structure and function of the major organs of various human body systems; 3. demonstrate an understanding of the structure and function of human body systems and interactions within and between systems. This activity would also fit with the Healthy Eating section of the Health strand for elementary students. If you do this activity it is good to cut up some extra bananas or bring some extra graham crackers for children to eat who might be hungry. Before the activity (e.g. day/night before): • cut the legs off the pantyhose (e.g. cut where the leg meets the crotch so you have two separate ‘legs’ with the toes intact) • make holes in the Dixie-­‐type cups that will act as the large intestine • get your bile read by mixing green food colouring with water • cut out digestive system parts for the art work (optional) • if not doing the art work, photocopy the worksheet Before you start: 1. Cut garbage bags so you can spread them out on the floor or use a large piece of plastic. You will need to cut as many as is needed for the size of group you have. Tape these to the floor with masking tape. 2. Have the children get a partner 3. Place enough materials out on the floor or surface you are using for each pair (e.g., 2 graham crackers (they can each chew), 1/3 of a banana, 1 dixie cup ¾ filled with water, 1 dixie cup with a small hole in the bottom, 1 plastic baggie, 1 leg of a pantyhose stocking, scissors) Materials needed 1 container (small cup, bottle) with water and green food colouring (bile) 1 pipette or syringe (to squirt the bile into the small intestine) about a cup of water (to represent saliva) garbage bags or a large piece of plastic masking or duct tape per pair of students 1/3 banana 2 graham crackers 1 plastic baggie (medium Ziplock or equivalent work well) 1 pair of scissors 1 Dixie-­‐type cup (3 oz) with a small hole (roughly the diameter of a pencil is good) 1 Dixie-­‐type cup (3/4 filled with water) 1 leg of a pair of pantyhose (open at one end and closed at the toe end) Art work Card stock of any colours – 1 full sheet per student plus enough card stock to cut out different parts of the digestive system Glue or tape Pencils to label parts Introduce the digestive system using pictures of the digestive system and asking the class what they already know using the questions below as a guide (some answers in square brackets]. Guiding questions and answers What does the digestive system start with? [mouth] What in the mouth helps us break down our food? [teeth – chewing into smaller bits; tongue – moves food around and pushes it into our esophagus; saliva/spit – starts the breakdown of carbohydrates] What kinds of foods are carbohydrates? [sugars, crackers, breads, cereals, fruits, etc.] Okay, so our food gets mixed with saliva and gets broken down into smaller bits and then pushed to the back of our throat where we swallow. What are the two other main types of foods? [proteins and fats] [proteins – meats, eggs, beans, tofu etc. and fats – butter, mayonnaise, French fries, etc.] Today in our model we will use our hands to represent our mouth. So when we “chew” our graham cracker, we will do so in our hand (not our mouth) Where does the food go when we swallow? [esophagus – a long tube with muscles that push our food from our mouth to the next organ in the digestive system (don’t tell them what that next organ is but you could show it on the picture); the pushing of the food by the muscles is called peristalsis; no digestion happens in the esophagus – it’s just a transport tube] We aren’t using an esophagus in our model today (mainly because the food often gets stuck but you could try a toilet paper tube if you wanted) What is the organ at the bottom of the esophagus? [stomach] What does the stomach do? [acids contained in the stomach do a little breaking down of the food – mostly proteins, but the main purpose of the stomach is to turn the food to liquid so it’s ready for what happens in the next part of the digestive system] Today in our model we’ll use a plastic baggie to represent our stomach and the cup of water to represent acids. (note: each part of the digestive system has valves/sphincters at the top/beginning and bottom/end that open and close as food passes through) What is the next part of the digestive system called? [small intestine] Why do you think it is called the small intestine and why do you think it is good to be very long? [even though it’s very long, it’s diameter is much less than the large intestine. This is where most of the digestion of fats, proteins and carbohydrates takes place. The top ~1/3 of your small intestine is where a special liquid comes in to break down fats – it’s greenish. Does anyone know what it is called? [bile] [Bile, is made in the liver and stored in the gallbladder and enters the small intestine through small tubes called ducts.] [other chemicals called enzymes also enter the small intestine (e.g. through the pancreas) and these help to make the digestion occur more quickly)] Why do we need nutrients? [bone growth and repair, energy for our muscles to work and our brain to think, needed for breathing – we need sugars for example) For our model today we’ll use the pantyhose leg as our small intestine and you will have to pour the contents of your stomach into the pantyhose without letting it go all the way down first so bile can be added (show them how to do this now or when doing the activity). Okay, now we’re at the last part/organ of our digestive system – what is it? [large intestine] What does the large intestine do? [water is absorbed back into our bodies; eliminates undigested food; bacteria in our large intestine help to make certain vitamins like Vitamin K which helps our blood to clot when we get a cut] Our large intestine in our model is the cup with the hole. Why is there a hole? [anus – where your poop/stool leaves your body; anus is a word that for some reason we are reluctant to say so I make them all say it and then say it again and maybe even one more time – it’s funny but it also makes them a bit more comfortable saying the proper term] Okay, let’s put this all together and follow our bananas and graham crackers through the model digestive system we have. Get them on the floor around the plastic if they are not already. Remind them to do everything over the garbage bags and not over their knees or parts of the floor with no bags on it. Have the children ‘chew’ the graham cracker by placing in their hand and squishing it (chewing) They should keep the cracker bits in their hand just as they would their real mouth. Pour or pipette a bit of water (saliva) into each of their hands as they are ‘chewing’. They should end up with a ball of food (bolus) when they are done ‘chewing’ just like we do in our mouths. [note: if you tell them you were up all night spitting into the jar or container with the water in it just so they could have some saliva, it grosses them out and adds to the activity]. Remind them or ask them what food type starts to break down in the mouth [carbohydrates]. We don’t have anything to simulate the esophagus but you could try some long paper towel tubes and see if they work or just tell them we don’t have one in this model but we’ll pretend the ball of food went down the esophagus. Have them put the ball of food into the baggie (by opening the ziplock at the top represent the valve between the esophagus and the stomach called the cardiac sphincter). Add the banana, both of their chewed up graham crackers, and the water from the cup (stomach acid) into the bag (stomach). Have them seal the bag tight (close the cardiac sphincter/valve to the stomach) without much air in the bag. Ask what happens if there is too much air in the bag (stomach)? They burb, belch, whatever they want to call it. Some will say they fart but that’s what happens when they have air in their intestine. Have them smush up the food and water in the stomach (until it’s fairly liquid and no big chunks). The stomach does this vigorously so show them how to squeeze it vigorously without breaking the baggie. While they are doing this you can say some more digestion takes place here of mainly proteins but most of it takes place in the next part of the digestive system (the small intestine – especially the top part fo the small intestine called the duodenum). At this point someone will likely not have completely closed their bag and the food will shoot out the top valve (ask them what’s happened? They just vomited. If everyone has their bag closed you can ask them what would happen if the food came out the top valve because perhaps it was damaged and didn’t close properly). Food stays in your stomach about 6 hours. Have them cut a hole in the bottom of the bag (valve called the pyloric sphincter) and pour it into only the top 1/3 of the panty hose leg. This will take 2 people. One cuts the hole in the bag and the other holds the panty hose leg open and places their other hand to keep the food going through the whole leg [you’ll have to experiment with this to know what I mean]. You don’t want them to squeeze the food through the pantyhose yet so let them know that. When they have the food in the top 1/3 of the panty hose leg, use the pipette to squirt the water with the food colouring (bile or bile salts) in and say you are squirting in bile which helps to break down fats (like dish washing detergent does on our dishes). Also let them know that most of the digestion takes place here. Have them squeeze the food through the pantyhose – it’s messy (representing the small intestines and the liquid coming out of the stocking represents the nutrients going to the rest of the body). So now the body has absorbed the nutrients through the blood stream. At the end of the panty hose leg they will need to cut another valve (ileocecal sphincter), so the food can go into the large intestine (cup with the hole in it). Finally have them squeeze the food into the cup (representing the large intestine). Talk about how there are good bacteria here that help make vitamins (especially vitamin K) and more water is absorbed into the body here. Then have them close the top of the cup and squeeze their waste through the hole (anus/anal sphincter) and poop out the undigested food! To clean up, remove the scissors and wash them. You can reuse the cups if they are in good shape or compost them along with the bananas. Then untape the bags/plastic and roll them up and throw the whole batch out into a new garbage bag. After giving them time to wipe their hands (sometimes I have a tub of water so they can dip their hands in before using the paper towel), go through the digestive system using the pictures again; or have them do the workshop, or make the digestive system using a piece of cardstock and the cut out digestive system parts and have them label each part and include a short explanation of what each part does.